The synthesis of rRNAs and tRNAs is intimately linked with cell division through the function of tumor suppressors (e.g. p53 and Rb) and oncogenes (e.g. c-myc). The transforming forms of these proteins directly target and up-regulate transcription by RNA polymerases (pols) I and III along with the expression of important cell cycle regulators. The Maf1 protein is a unique regulator of transcription whose properties in human cells are similar to p53 and Rb. Human Maf1 is a candidate tumor suppressor that negatively regulates transcription by all three nuclear RNA polymerases. How Maf1 achieves its effects on transcription is not understood and is complicated by the fact that the protein does not contain any motifs of known function. In S. cerevisiae, Maf1 is essential for repressing transcription by RNA polymerase III and functions to integrate the responses from multiple nutritional and stress signaling pathways that coordinately regulate ribosome and tRNA synthesis. These pathways, like Maf1 itself, are not well defined. The universal requirement for Maf1 in pol III transcriptional repression in yeast provides an extraordinarily valuable model for understanding the pathways and mechanisms regulating ribosome and tRNA synthesis and the biochemical function of this novel signal integrator. Accordingly, the long-term goal of this research is to understand Maf1 structure/function relationships, its interactions with regulatory targets and its interactions with upstream signaling molecules that operate via posttranslational mechanisms to affect Maf1-dependent transcriptional repression. These aims will be achieved through biochemical studies in well-defined in vitro systems and through the application of an innovative method for phosphopeptide identification. In addition, powerful genome-wide and systematic genetic and biochemical approaches will be used to identify protein kinases and other molecules involved in signaling repression by Maf1. Finally, our understanding of the function and regulation of Maf1 will be advanced by the determination its three-dimensional structure. PUBLIC HEALTH RELEVANCE: Maf1 is a potential tumor suppressor that negatively regulates transcription by all three nuclear RNA polymerase in mammalian cells. In yeast, Maf1 is an essential mediator of transcriptional repression by RNA polymerase III and integrates the responses from multiple nutritional and stress signaling pathways that coordinately regulate ribosome and tRNA synthesis. Our genetic, biochemical and structural studies on on Maf1 will enhance understanding of fundamental cellular processes that are likely to impact cancer biology.